1. Field of the Invention
The present invention relates to jet cutting systems and, more particularly, to a method of and apparatus for producing a generally axially disposed erosive cutting jet stream for drilling, boring and the like.
2. History of the Prior Art
The prior art is replete with designs for mechanical cutting systems used to break, fracture and/or shear formations for the penetration thereof. Examples of such systems include modern-day drill bits of the type used for drilling deep well bores for the oil and gas industries. The most critical problem associated with the mechanical cutting of formations is untimely stress corrosion or thermal degradation failure of the materials used as the cutting means. Such material failure limits the ability of the operator to transfer high mechanical energy to the mechanical cutters. These problems create financial as well as physical limitations for commercially available drilling systems. In essence, the subterranean formation must be capable of cost effective penetration, which requires efficient energy transfer.
The search for a more efficient energy transfer system has resulted in a number of recent inventions and developments in drilling, boring and cutting systems. For example, the development of hydraulic erosion jetting mechanisms has, over the last 50 years, been the subject of increased interest. This design direction is due to the attributes of hydraulic erosion jetting, which include more efficient energy conversion to the work surface and a potentially ideal working medium, typically water, which is in great abundance and therefore economically expendable. Moreover, the technique is conceptually simple.
Hydraulic erosion of earthen formations is a technology that has been analyzed and reported in numerous publications. The erosion takes place by employing various failure mechanisms of the work surface induced by action of the liquid jet. The types of failure mechanisms that have been reported include; (1) failure of porous rock due to stress induced through liquid filled pore spaces of the rock brought about by impacting the liquid contained in the pore space; (2) formation failure by crack propagation and/or extension due to hydraulic fracture forces occurring when a liquid filled fracture is forced to close after an initial mechanical force is released; (3) liquid jet droplet impingement that erodes the cementation between formation grains thereby loosening and dislodging the harder formation grains. This last stated technique is known as Soft Erosion and is the typical mechanism present when eroding formations where the impinging jet stagnation pressures do not exceed the threshold pressures required to fracture the rock and thereby force large scale permeability in the in situ formation.
Other types of formation failure include (4) droplet impingement, known as Hard Erosion, that fractures the rock grains and the cementation by exceeding the threshold pressures necessary to fracture the formation grains and force large scale permeability by breaking the individual grains away from the formation; and (5) liquid jet induced pressure reversals that allow the in situ formation pore pressures to force tensile failure of the cementation holding rock grains together.
Prior art investigations and applications of erosive jet cutting have shown that liquid jets can be very effective in eroding rocks. The investigations have covered the broad modes of jet operation classed as continuous jets, interrupted jets, cavitating jets and abrasive particle jets. In each broad category there are a multiplicity of variations of the jets that have been investigated to focus on a predominant operational feature of the jet mode. Examples of these investigations are found in the following articles: "Tests Show Jet Drilling Has Promise", Feenstra, R. , et al, The Oil and Gas Journal, Jul. 1, 1974, "The Effects of Porosity on Hydraulic Rock Cutting", Crow, S. C., International Journal of Rock Mechanics, Mining, Science & Geomechanics Abstract, Vol. 11, pp. 103-105. Pergamon Press 1974 and "A Model Study of the Water Pressure Distribution in a Crack when Impacted by a High Pressure Water Jet", Mazurkiewicz, Dr. M. et al, 8th International Symposium on Jet Cutting Technology, Durham, England: 9-11 September, 1986. In addition, references to cavitation and particle abrasion, respectively, may be seen in the following articles: "The Development of Structured Cavitating Jets for Deep-Hole Bits" by Virgil E. Johnson, Jr., Georges L. Cahine, William Lindenmuth, Andrew F. Carr and Gary S. Frederick, Hydronautics, Incorporated and George J. Giacchino, Jr. NL/HYCALOG/NL Industries, Inc., Society of Petroleum Engineers or AIME Paper 11060, 1982; and "New Gulf Method of Jetted-Particle Drilling Promises Speed and Economy," The Oil and Gas Journal Jun. 21, 1971.
A number of problems are associated with erosive jet cutting systems. One of the problems that limits the optimum performance of the jet has been the inability to provide reliable means for maintaining a specific distance between the jet nozzle and the target formation. In prior art designs, it has been deemed necessary to control the distance between the nozzle and the target formation in order to properly focus the energy of the jet streams. In order to address this problem, most nozzles have been recessed from the cutting surface by several nozzle diameters in order to allow the nozzle to survive the rigors of the cutting environment while others have been recessed to allow maturation of the erosive jet mode to develop. It has been noted, however, that the splash back erosion against the tool caused by the jet action then becomes a serious problem. Additionally, there is typically an exponential energy decay with increased standoff distances. A number of prior art patents have addressed these various concerns, and the teachings of these patents are illustrative of several problems in erosive cutting jet systems.
U.S. Pat. No. 4,787,465, entitled Hydraulic Drilling Apparatus and Method, is a 1988 patent teaching a drilling apparatus producing a whirling mass of pressurized cutting fluid to create a high-velocity cutting jet. The cutting action is enhanced by abrasive material in the drilling fluid. This technology is further discussed in U.S. Pat. No. 4,852,668, which is a 1989 patent issued to the same inventors. The cutting nozzles disclosed in these patents employ an axial conical spray that predominantly uses the development of a thin sheet of high speed liquid drops that develop within the conical spray and erode through liquid drop impingement of the target formation granule cementation and thereby dislodge formation grains as discussed above. These grains are then carried into a reentry torodial flow motion, which is perpendicular to the axis of the conical spray, that further uses the grains for an in situ abrasive to abrade and dislodge further particles. The stated purpose of this conical jet is to hydraulically drill a hole of a diameter larger than the drill head and its supply/transport tube without rotating the system. This aspect is more fully set out in the article "Conical Water Jet Drilling", Dickenson, W. et al, Proceedings of the Fourth U.S. Water Jet Conference.
Various attempts to combine the positive aspects of mechanical cutting means and hydraulic erosion jetting means have also been reported. Several references may be seen in "Five Wells Test High-Pressure Drilling", Deily, F. H. et al, The Oil and Gas Journal, Jul. 4, 1977; "Laboratory Testing of High Pressure, High Speed PDC Bits"--W. C. Maurer and W. J. McDonald, Maurer Engineering, Inc.; J. H. Cohen, Drilling Research Center, Inc.; J. W. Neudecker Jr., Los Almos National Laboratory; and D. W. Carroll, U.S. Air Force--SPE Paper 15615, "Water-Jet-Assisted Drag Bit Cutting in Medium-Strength Rock", Geier, J. E. et al, United States Department of the Interior Information Circular 9164 and "High Pressure Drilling System Triples ROPS, Stymies Bit Wear" Mike Killalea, Editor--Drilling, March/April 1989.
Additional development efforts in combining mechanical cutting and hydraulic erosion jetting means are seen in U.S. Pat. No. 3,838,742 issued to Juvkam-Wold and U.S. Pat. No. 4,391,339 issued to Johnson. The Juvkam-Wold patent teaches the use of a fluid/mechanical system incorporating abrasive resistant nozzles recessed in a mechanical drill bit adapted for discharging a high velocity stream of abrasive laden liquid through the nozzles. The Johnson patent teaches an improved technique utilizing recessed nozzles adjacent mechanical cutting surfaces, wherein the nozzles discharge a cavitating liquid jet. This patent, which references the Juvkam-Wold patent, further teaches one technique of maintaining a controlled distance between the cavitating jet nozzles and the surface to be cut by using exposed diamond wear buttons and a pre-select nozzle recess distance wherein maximum cavity collapse is said to occur. The recess also serves an apparent purpose of protecting the nozzle. A further discussion of the use of structured shedding vortex rings created in the shear zone between the jet and the spent liquid in the hole, wherein vapor cavities are formed, may also be seen. The application of vortex ring cavitation has thus been recognized to be effective in such fluid/mechanical cutting systems.
As referenced above, the combination of high speed fluid jet cutting in mechanical drilling systems has clearly been the subject of continued development for cutting systems. This type of combination has been shown to demonstrate superior efficiencies when compared to purely hydraulic erosion drilling means. However, a number of problems still plague the industry, which problems prevent a reliable and efficient high-speed cutting jet. It would be an advantage, therefore, to utilize the positive aspects of high-speed jet cutting in a fluid/mechanical system that is both reliable and devoid of the critical problems of the prior art. The present invention provides such a system by utilizing a high-speed spinning jet stream with a single or multiple axial plenum erosive cutter produced from the end of a tapered housing.